Thin film transistors and semiconductor device

ABSTRACT

The TFT has a channel-forming region formed of a crystalline semiconductor film obtained by heat-treating and crystallizing an amorphous semiconductor film containing silicon as a main component and germanium in an amount of not smaller than 0.1 atomic % but not larger than 10 atomic % while adding a metal element thereto, wherein not smaller than 20% of the lattice plane { 101 } has an angle of not larger than 10 degrees with respect to the surface of the semiconductor film, not larger than 3% of the lattice plane { 001 } has an angle of not larger than 10 degrees with respect to the surface of the semiconductor film, and not larger than 5% of the lattice plane { 111 } has an angle of not larger than 10 degrees with respect to the surface of the semiconductor film as detected by the electron backscatter diffraction pattern method.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. application Ser.No. 09/874,204, filed on Jun. 6, 2001, now U. S. Pat. No. 6,690,068,which claims the benefit from foreign priority applications filed inJapan, as serial number 2000-176173, filed Jun. 12, 2000, serial number2000-176188, filed Jun. 12, 2000, serial number 2000-177641, filed Jun.13, 2000, and serial number 2000-177652, filed Jun. 13, 2000. Thisapplication claims priority to all of these applications, and all ofthese applications are incorporated by reference.

BACKGROUND OF THE INVENTION

1. [Field of the Invention]

This invention relates to thin film transistors using a semiconductorfilm of crystals that are collected having various azimuths (hereinafterreferred to as crystalline semiconductor film) as represented by apolycrystalline silicon film, and a semiconductor device formed by usingthe above thin film transistors. In particular, the invention relates toa semiconductor film forming a channel-forming region, a source regionand a drain region of a thin film transistor and to a semiconductordevice mounting the above thin film transistors. In this specification,the semiconductor device refers to devices that work by utilizingsemiconductor characteristics as a whole inclusive of display devices asrepresented by a liquid crystal display device and semiconductorintegrated circuits (microprocessors, signal processing circuits andhigh-frequency circuits).

2. [Prior Art]

There has been developed a technology for fabricating thin filmtransistors (hereinafter abbreviated as TFTs) by forming a crystallinesemiconductor film on a glass substrate or on a quartz substrate.Application of this technology has been forwarded in a field of flatpanel displays as represented by an active matrix liquid crystal displaydevice. TFTs are used as switching elements in the pixels or as elementsfor forming a driver circuit formed in the peripheries of the pixels.

Silicon is chiefly used as a material of a crystalline semiconductorfilm for forming the channel-forming regions, source regions, drainregions or low-concentration drain (lightly doped drain: LLD) regions inactive regions of TFTs. The silicon film having a crystalline structure(hereinafter referred to as crystalline silicon film) is formed bysubjecting an amorphous silicon film deposited on a substrate by aplasma CVD method or a low pressure CVD method to the heat treatment orto the irradiation with a laser beam (hereinafter referred to as lasertreatment in this specification).

In conducting the heat treatment, however, the heating must be effectedat a temperature of not lower than 600° C. for not less than 10 hours tocrystalize the amorphous silicon film. The above treating temperatureand the treating time are not necessarily suitable from the standpointof productivity of the TFTs. When a liquid crystal display device istaken into consideration as an applied product using TFTs, a heatingfurnace of a large size is necessary to cope with an increase in thearea of the substrate, not only consuming energy in large amounts in thesteps of production but also making it difficult to obtain homogeneouscrystals over a wide area. In the case of the laser treatment, it isdifficult to obtain homogeneous crystals due to the lack of stability inthe output of the laser oscillator. Dispersion in the quality ofcrystals could become a cause of dispersion in the TFT characteristics,and deteriorates the quality of display of the liquid crystal displaydevices and the EL display devices.

There has also been proposed a technology for forming a crystallinesilicon film through the heat treatment at a temperature lower than thetemperatures employed thus far by introducing, into the amorphoussilicon film, metal elements that assist the crystallization of silicon.According to, for example, Japanese Patent Application (Kokai) Nos.7-130652 and 8-78329, a crystalline silicon film is obtained by the heattreatment conducted at 550° C. for 4 hours by introducing such a metalelement as nickel into the amorphous silicon film.

In the crystalline silicon film formed by the above conventionalmethods, however, the planes of crystalline azimuth exist in a randomfashion, and the ratio of orientation is low for particular crystallineazimuths. The crystalline silicon film obtained by the heat treatment orthe laser treatment permits plural crystalline particles to beprecipitated and oriented on {111}. Even when limited to the planeazimuth, however, the ratio of orientation did not exceed 20% of thewhole film.

When the ratio of orientation is low, it is almost impossible tomaintain continuity of lattice on the crystalline grain boundaries wherethe crystals of different azimuths abut to each other, and it isestimated that unpaired bonds are formed much. The unpaired bonds on thegrain boundaries could become centers of trapping the carriers(electrons/holes) accounting for a drop in the carrier transportproperty. That is, since the carriers are scattered and trapped, a TFThaving a high electric-field mobility cannot be expected despite the TFTis fabricated by using the above crystalline semiconductor film.Besides, since the crystalline grain boundaries exist in a randomfashion, it is difficult to form the channel-forming region usingcrystalline particles having a particular crystalline azimuth, andelectric characteristics of the TFT tend to become dispersed.

SUMMARY OF THE INVENTION

It is an object of this invention to provide means for solving theabove-mentioned problems, and to provide TFTs using a crystallinesemiconductor film which is obtained by crystallizing an amorphoussemiconductor film and is highly oriented, as well as to provide asemiconductor device mounting the above TFTs.

This invention provides a TFT having a channel-forming region formed ofa crystalline semiconductor film obtained by heat-treating andcrystallizing an amorphous semiconductor film containing silicon as amain component and germanium in an amount of not smaller than 0.1 atomic% but not larger than 10 atomic % (preferably, not smaller than 1 atomic% but not larger than 5 atomic %) while adding a metal element thereto,wherein an orientation ratio of the lattice plane {101} is not smallerthan 20% and the lattice plane {101} has an angle of not larger than 10degrees with respect to the surface of the semiconductor film, and anorientation ratio of the lattice plane {001} is not larger than 3% andthe lattice plane {001} has an angle of not larger than 10 degrees withrespect to the surface of the semiconductor film, and an orientationratio of the lattice plane {001} is not larger than 5% and the latticeplane {111} has an angle of not larger than 10 degrees with respect tothe surface of the semiconductor film as detected by the electronbackscatter diffraction pattern method.

The invention further provides a TFT having a channel-forming regionformed of a crystalline semiconductor film obtained by heat-treating andcrystallizing an amorphous semiconductor film containing silicon as amain component and germanium in an amount of not smaller than 0.1 atomic% but not larger than 10 atomic % (preferably, not smaller than 1 atomic% but not larger than 5 atomic %) while adding a metal element thereto,wherein an orientation ratio of the lattice plane {101} is not smallerthan 5% and the lattice plane {101} has an angle of not larger than 5degrees with respect to the surface of the semiconductor film, anorientation ratio of the lattice plane {001} is not larger than 3% andthe lattice plane {001} has an angle of not larger than 10 degrees withrespect to the surface of the semiconductor film, and an orientationratio of the lattice plane {001} is not larger than 5% and the latticeplane {111} has an angle of not larger than 10 degrees with respect tothe surface of the semiconductor film as detected by the electronbackscatter diffraction pattern method.

The invention further provides a TFT having a channel-forming regionformed of a highly oriented crystalline semiconductor film having athickness of from 20 nm to 100 nm and containing nitrogen and carbon atconcentrations of smaller than 5×10¹⁸/cm³, containing oxygen at aconcentration of smaller than 1×10¹⁹/cm³, and containing the metalelement at a concentration of smaller than 1×10¹⁷/cm³.

The invention further provides a semiconductor device having achannel-forming region formed of a semiconductor film obtained byheat-treating and crystallizing an amorphous semiconductor filmcontaining silicon as a main component and germanium in an amount of notsmaller than 0.1 atomic % but not larger than 10 atomic % (preferably,not smaller than 1 atomic % but not larger than 5 atomic %) while addinga metal element thereto, wherein an orientation ratio of the latticeplane {101} is not smaller than 20% and the lattice plane {101} has anangle of not larger than 10 degrees with respect to the surface of thesemiconductor film, and an orientation ratio of the lattice plane {001}is not larger than 3% and the lattice plane {00l} has an angle of notlarger than 10 degrees with respect to the surface of the semiconductorfilm, and an orientation ratio of the lattice plane {001} is not largerthan 5% and the lattice plane {111} has an angle of not larger than 10degrees with respect to the surface of the semiconductor film asdetected by the electron backscatter diffraction pattern method.

The invention further provides a semiconductor device having achannel-forming region formed of a semiconductor film obtained byheat-treating and crystallizing an amorphous semiconductor filmcontaining silicon as a chief component and germanium in an amount ofnot smaller than 0.1 atomic % but not larger than 10 atomic %(preferably, not smaller than 1 atomic % but not larger than 5 atomic %)while adding a metal element thereto, wherein an orientation ratio ofthe lattice plane {101} is not smaller than 5% and the lattice plane{101} has an angle of not larger than 5 degrees with respect to thesurface of the semiconductor film, an orientation ratio of the latticeplane {001} is not larger than 3% and the lattice plane {001} has anangle of not larger than 10 degrees with respect to the surface of thesemiconductor film, and an orientation ratio of the lattice plane {001}is not larger than 5% and the lattice plane {111} has an angle of notlarger than 10 degrees with respect to the surface of the semiconductorfilm as detected by the electron backscatter diffraction pattern method.

The invention further provides a semiconductor device having achannel-forming region formed of a highly oriented crystallinesemiconductor film having a thickness of from 20 nm to 100 nm andcontaining nitrogen and carbon at concentrations of smaller than5×10¹⁸/cm³, containing oxygen at a concentration of smaller than1×10¹⁹/cm³, and containing the metal element at a concentration ofsmaller than 1×10¹⁷/cm³.

The metal element that is added is one or more of those selected fromFe, Co, Ni, Ru, Rh, Pd, Os, Ir, Pt, Cu and Au. The amorphous siliconfilm to which the metal element is added is heat-treated to thereby forma compound (silicide compound) of silicon with the metal element. Thiscompound then diffuses to assist the crystallization. Germanium that isadded to the amorphous silicon does not react with this compound butstays in the peripheries thereof to build up local strain. The strainworks to increase the critical radius of the formation of nuclei and,hence, to decrease the density of the formation of nuclei. The strainfurther limits the orientation of crystals.

To produce the above-mentioned action, it has been learned throughexperiment that germanium needs to be added in an amount of not smallerthan 0.1 atomic % but not larger than 10 atomic % (preferably, notsmaller than 1 atomic % but not larger than 5 atomic %). When germaniumis added in amounts larger than the above range, nuclei are formedspontaneously and conspicuously (crystalline nuclei that are notdependent upon the compound of the added metal element) as an alloy ofsilicon and germanium, making it difficult to increase the ratio oforientation of the obtained crystalline semiconductor film. Whengermanium is added in too small amounts, strain does not build up to asufficient degree making it difficult to increase the ratio oforientation, either.

When the amorphous semiconductor film is crystallized, the volume of thefilm contracts due to the rearrangement of atoms if viewedmacroscopically. As a result, tensile stress occurs in the crystallinesemiconductor film formed on the substrate. Upon containing germaniumhaving an atomic radius larger than that of silicon at a concentrationof 0.1 to 10 atomic %, preferably, 1 to 3 atomic %, however, thecontraction of volume due to the crystallization is suppressed, and asmall internal stress occurs. That is, upon containing germanium at aconcentration as contemplated by this invention, the strain in thecrystalline semiconductor film can be relaxed.

The distribution of crystalline azimuths can be found by using anelectron backscatter diffraction pattern (EBSP). The EBSP is a method ofanalyzing the crystalline azimuth from the backscattering of primaryelectrons by providing a scanning electron microscope (SEM) with aspecial detector (hereinafter, this method is referred to as EBSP methodfor convenience). FIG. 2 is a diagram illustrating the principlethereof. An electron gun (Schottky field-effect emission electron gun)201, a mirror 202 and a sample chamber 203 are constituted in the samemanner as those of an ordinary scanning electron microscope. To measurethe EBSP, a stage 204 is tilted at an angle of about 60 degrees, and asample 209 is installed. In this state, a screen 205 of a detector 206is inserted so as to face the sample. Reference numeral 207 indicates anelectron beam; 208, a backscattered electron.

Here, when an electron ray falls on the sample having a crystallinestructure, non-elastic scattering also takes place on the back sidethereof, and there can be also observed a linear pattern (generallycalled Kikuchi image) specific to the crystalline azimuth due to Braggdiffraction in the sample. According to the EBSP method, the Kikuchiimage reflected on the detector screen is analyzed to find thecrystalline azimuth of the sample.

FIG. 3 illustrates a crystalline semiconductor film 302 of apolycrystalline structure formed on a substrate 301. The crystallinesemiconductor film 302 has a prerequisite in that each crystallineparticle therein has a different crystalline azimuth. Upon repeating(mapping) the azimuthal analysis while moving a position of the samplewhere the electron beam falls, the data related to the crystallineazimuth or to the orientation can be obtained concerning the planarsample. The thickness of the incident electron beam 303 varies dependingupon the type of the electron gun of the scanning electron microscope.In the case of the Schottky electric-field emission electron gun, anelectron beam of as very fine as 10 to 20 nm can be projected. In themapping, more highly averaged data of crystal orientation are obtainedwith an increase in the number of the measuring points or with anincrease in the area of the measured region. In practice, about 10000points (a gap of 1 μm) to about 40000 points (0.5 μm) are measured overa region of 100×100 μm². Reference numeral 304 indicates a backscatteredelectron.

When the crystalline azimuths of the crystalline particles are all foundby mapping, the state of crystal orientation for the film can beexpressed in a statistic manner. FIG. 4A is a diagram illustrating backpoles found by the EBSP method. The diagram of the back poles isfrequently used for displaying the preferential orientation of apolycrystalline substance and collectively represents which latticeplane a particular plane (surface of the film, here) of the sample is inagreement with.

A fan-shaped frame of FIG. 4A is usually called a standard triangle inwhich are included all indexes of the cubic crystal system. The lengthin this diagram corresponds to an angle in the crystalline azimuth. Forexample, an angle of 45 degrees is defined by {001} and {101}, an angleof 35.26 degrees is defined by {101} and {111}, and an angle of 54.74degrees is defined by {111} and {001}. White dotted lines representranges of shearing angles of 5 degrees and 10 degrees from {101}.

FIG. 4A is the one in which all measuring points (11655 points in thisexample) in the mapping are plotted within the standard triangle. Itwill be learned that the density is high near the point {101}. FIG. 4Bshows the concentration of such points using contour lines. These arethe values of an azimuth distribution function, and the concentration(density of points of FIG. 4A) is represented by a contour line in thecase when a random orientation is presumed. Here, the values representmagnifications of when it is presumed that the crystalline particles areoriented in a quite orderless manner, i.e., when the points are evenlydistributed in the standard triangle, and are the values withoutdimension.

When it is learned that the crystalline particles are preferentiallyoriented to a particular index (here, {101}), the ratio of the number ofcrystalline particles collected near the index is indicated by anumerical value, so that the degree of preferential orientation can beeasily imagined. In the diagram of back poles shown in FIG. 4A, forexample, the ratio of the number of points present in a range between ashearing angle of 5 degrees and a shearing angle of 10 degrees from{101} (indicated by white dotted lines in the drawing) to the totalnumber of the points can be expressed as a ratio of orientation incompliance with the following formula.

$\begin{matrix}{{\{ 101 \}\mspace{11mu}{Ratio}\mspace{14mu}{of}\mspace{14mu}{orientation}} = {{number}\mspace{14mu}{of}\mspace{14mu}{measured}\mspace{14mu}{points}\mspace{14mu}{within}\mspace{14mu}{an}\mspace{14mu}{allowable}\mspace{14mu}{angle}\mspace{14mu}{between}\mspace{14mu}{the}\mspace{14mu}{lattice}\mspace{14mu}{plane}{\;\;}\{ 101 \}\mspace{14mu}{and}\mspace{14mu}{the}\mspace{14mu}{film}\mspace{14mu}{surface}\text{/}{total}\mspace{14mu}{number}\mspace{14mu}{of}\mspace{14mu}{the}\mspace{14mu}{measured}\mspace{14mu}{points}}} & \lbrack {{Formula}\mspace{14mu} 1} \rbrack\end{matrix}$

This ratio can be explained in a manner as described below. When thedistribution is concentrated near {101} as in FIG. 4A, the individualparticles in a real film have an azimuth <101> nearly perpendicular tothe substrate as shown in FIG. 6 but are expected to be arranged beingfluctuated thereabout. The allowable values of the angle of fluctuationare set to be 5 degrees and 10 degrees, and the ratio of those smallerthan these values are numerically expressed. Reference numeral 601indicates a substrate; 602, a crystalline semiconductor film. In FIG. 5,for example, the azimuth <101> 505 of a given crystalline particle isnot included in an allowable range of 5 degrees 503 but is included inan allowable range of 10 degrees 504. In the data appearing later, theallowable shearing angles are set to be 5 degrees and 10 degrees asdescribed above, and the ratio of crystalline particles satisfying thisis expressed. Reference numeral 501 indicates surface of a film; 502, aperpendicular line of surface.

In the diagram of back poles shown in FIG. 4A, the vertexes are {101},{111} and {001}, and the other plane azimuth appears as the shearingvalue increases relative to {101}. As the shearing angle from {101}becomes 30 degrees, then, {112} develops. When the ratio of existence ofcrystalline azimuth is to be determined by the EBSP, therefore, theallowable shearing angle must be determined for the crystallineparticles that are distributed in a fluctuated manner so as not toinclude other indexes. The present inventors have discovered that theratio of existence of crystalline particles oriented in a particularazimuth can be quantitatively expressed by collecting the data whilesetting the allowable shearing angle to be smaller than 10 degrees orsmaller than 5 degrees.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of back poles of a crystalline semiconductor film ofthe invention found by the EBSP method;

FIG. 2 is a diagram illustrating the constitution of an EBSP device ofthe present invention;

FIG. 3 is a diagram illustrating the concept of measuring a sample bythe EBSP of the present invention;

FIGS. 4A and 4B are diagrams of back poles obtained from the EBSP dataof the present invention;

FIG. 5 is a diagram illustrating shearing angles from the {101}orientation of the present invention;

FIG. 6 is a diagram illustrating the fluctuation in the <101> azimuth ofcrystalline particles preferentially oriented near {101} of the presentinvention;

FIGS. 7A-7D are diagrams illustrating a method of forming a crystallinesemiconductor film of Embodiment 1;

FIGS. 8A and 8B are diagrams illustrating a method of forming thecrystalline semiconductor film of Embodiment 2;

FIGS. 9A-9C are diagrams illustrating a method of forming thecrystalline semiconductor film of Embodiment 3;

FIGS. 10A-10C are diagrams illustrating a method of forming thecrystalline semiconductor film of Embodiment 4;

FIGS. 11A and 11B are diagrams illustrating a step of fabricating asemiconductor device of Embodiment 5;

FIGS. 12A-12C are diagrams illustrating a step of fabricating thesemiconductor device of the present invention;

FIG. 13 shows SIMS data expressing C, N and O concentrations of samplesby using SiH₄, GeH₄ and H₂ gases of the present invention;

FIG. 14 is a graph showing Ge concentrations of samples (SGN5) and(SGN10) measured by SIMS of the present invention;

FIG. 15 is a graph illustrating a relationship between the amount ofaddition of GeH₄ and the density of generation of crystalline nuclei ofthe present invention;

FIGS. 16A and 16B show X-ray diffraction patterns of samples (SN) and(SGN10) by the θ-2θ method of the present invention;

FIG. 17 is a diagram of back poles of the sample (SN) found by the EBSPmethod of the present invention;

FIG. 18 is a diagram of back poles of the sample (SN) found by the EBSPmethod of the present invention;

FIGS. 19A-19E are diagrams illustrating the steps of fabricating TFTs ofa CMOS structure of Embodiment 6;

FIGS. 20A-20E are diagrams illustrating examples of electronic devicesof Embodiment 8;

FIGS. 21A-21C are diagrams illustrating examples of electronic devicesof Embodiment 8;

FIGS. 22A-22D are diagrams illustrating an example of a projector ofEmbodiment 8;

FIGS. 23A-23E are diagrams illustrating a method of forming acrystalline semiconductor film of Embodiment 8;

FIG. 24A is a graph illustrating the concentrations of metal elementsmeasured by TXRF (Total Reflection X-ray Fluorescene Spectroscopy)before and after the gettering treatment and FIG. 24B os a diagramexplaining a measuring method of TXRF of Embodiment 7.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment Mode

This invention has a feature in that the crystalline semiconductor filmused as the channel-forming region of a TFT is the one containing, as amain component, silicon which is highly oriented on the {101} latticeplane. According to a representative embodiment for obtaining thecrystalline semiconductor film, a metal element is introduced into thesurface of an amorphous semiconductor film formed by a plasma CVD methodor a low pressure CVD method by using a gas of a hydride, a fluoride ora chloride of silicon atoms and germanium atoms in order to assist thecrystallization of the amorphous semiconductor film, and a crystallinesemiconductor film is formed by the heat-treatment by utilizing themetal element.

As the substrate for forming the crystalline semiconductor film, therecan be suitably used an alkali-free glass substrate such as an aluminaborosilicate glass or barium borosilicate glass. Typically, a #7059glass substrate or a #1737 glass substrate of Coning Co. is used. Therecan be further used a quartz substrate or a sapphire substrate. Or, aninsulating film may be formed on the surface of a semiconductorsubstrate of silicon, germanium, gallium, or arsenic to use it as asubstrate.

When the above glass substrate is used, a blocking layer of siliconnitride, silicon oxide or silicon nitride oxide is formed between theamorphous semiconductor film and the glass substrate. This preventsimpurity elements such as alkali metal elements contained in the glasssubstrate from diffusing into the semiconductor film. For example, SiH₄,NH₃ and N₂ are used as reaction gases in the plasma CVD method to form asilicon nitride film. Or, SiH₄, N₂O and NH₃ are used as reaction gasesto form a silicon nitride oxide film. The blocking layer is formedmaintaining a thickness of 20 to 200 nm.

The amorphous semiconductor film is formed on the substrate by theplasma CVD method, low pressure CVD method or by any other suitablemethod. When the plasma CVD method is applied, the reaction gas of SiH₄and GeH₄ or the reaction gas of GeH₄ diluted with SiH₄ and H₂ is addedand introduced into the reaction chamber and is decomposed by ahigh-frequency electric discharge of 1 to 200 MHz to deposit anamorphous semiconductor film on the substrate. The reaction gas maycontain Si₂H₆ or SiF₄ instead of SiH₄, or may contain GeF₄ instead ofGeH₄. Even when the low pressure CVD method is employed, a similarreaction gas may be used. Preferably, the reaction gas is diluted withHe, and an amorphous semiconductor film is deposited on the substrate ata temperature of 400 to 500° C. In any way, the gas used in thisinvention is the one that is highly purified to decrease theconcentrations of impurity elements such as oxygen, nitrogen, carbonthat may be trapped by the amorphous semiconductor film that isdeposited. The amorphous semiconductor film that is deposited has athickness in a range of from 20 to 100 nm.

The amorphous semiconductor film used in this invention contains siliconas a main component and germanium in an amount of not smaller than 0.1atomic % but not larger than 10 atomic % (preferably, not smaller than 1atomic % but not larger than 5 atomic %). The content of germanium canbe adjusted relying upon the mixing ratio of SiH₄ and GeH₄ used astypical reaction gases. The amorphous semiconductor contains nitrogenand carbon at concentrations of smaller than 5×10¹⁸/cm³ and oxygen at aconcentration of smaller than 1×10¹⁹/cm³, so that the amorphoussemiconductor film will not be adversely affected in the step ofcrystallization and that electric properties of the crystallinesemiconductor film that is formed will not be adversely affected.

A metal element is introduced into the surface of the thus formedamorphous semiconductor film to assist the crystallization of theamorphous semiconductor film. There can be used one or more kinds ofmetal elements selected from iron (Fe), nickel (Ni), cobalt (Co),ruthenium (Ru), rhodium (Rh), palladium (Pd), osmium (Os), iridium (Ir),platinum (Pt), copper (Cu) and gold (Au). These metal elements can beused for assisting the crystallization of the amorphous semiconductorfilm in any one of the inventions disclosed in this specification. Thesame and equal effect can be obtained by using any one of the abovemetal elements. Typically, however, nickel is used.

The portions into which the metal elements are introduced may be thewhole surface of the amorphous semiconductor film, slit-like surfaces ordot-like surfaces at suitable places on the surface of the amorphoussemiconductor film. In the former case, the place may be either thesurface on the substrate side of the amorphous semiconductor film or thesurface on the side opposite to the substrate. In the latter case, aninsulating film is preferably formed on the amorphous semiconductorfilm, and the metal element is introduced through openings formed in theinsulating film. There is no particular limitation on the size of theopenings, but the width may be 10 to 40 μm. The length in the lengthwisedirection may be arbitrarily determined to be, say, from several tens ofmicrons to several tens of centimeters.

There is no particular limitation on the method of introducing thesemetal elements and any method can be employed provided it forms a metalfilm on the surface of the amorphous semiconductor film or insidethereof. There can be employed, for example, sputtering method,vaporization method, plasma processing method (inclusive of plasma CVDmethod), adsorption method or a method of applying a solution of a metalsalt. The plasma processing method utilizes the metal element sputteredfrom a cathode in a glow-discharge atmosphere of an inert gas. Themethod of applying a solution of a metal salt is useful since it is easyfacilitating the adjustment of concentration of the metal element.

As the metal salt, there can be used various salts. As the solvent,there can be used water, alcohols, aldehydes, ethers or any otherorganic solvent, or a mixture of water and the organic solvents.Further, the solution is not necessarily the one in which the metal saltis completely dissolved therein but may be the one in which part orwhole of the metal salt is present in the state of a suspension.Whichever method is employed, the metal element is introduced beingdispersed on the surface or inside of the amorphous semiconductor film.

After the metal element is introduced by any one of the above methods,the amorphous semiconductor film is crystallized by utilizing the metalelement. The crystallization is effected by the heat treatment, or theirradiation with an intense light such as laser beam, ultraviolet ray orinfrared ray. The heat treatment only is enough for obtaining thecrystalline silicon film which is preferentially oriented in {101}.Preferably, however, the heat treatment is effected and, then, anintense light such as laser beam is projected. The laser treatment afterthe heat treatment repairs and extinguishes crystal defects left in thecrystalline particles, and is effective in improving the quality of thecrystals that are formed.

The heat treatment can be conducted over a range of 450 to 1000° C. Theupper limit of temperature is considered as an upper limit oftemperature which the substrate that is used can withstand. For example,a quart: substrate can withstand the heat treatment at 1000° C. When theglass substrate is used, however, the upper limit of temperature mustnot be higher than a distortion point thereof. When, for example, theglass substrate has a distortion point of 667° C., the upper limitshould be set to be about 660° C. The required time is suitably setdepending upon the heating temperature and the subsequent treatingconditions (e.g., whether the treatment is effected being irradiatedwith a laser beam). Suitably, however, the heat treatment is conductedat 550 to 600° C. for 4 to 24 hours. When the laser treatment follows,the heat treatment is conducted at 500 to 550° C. for 4 to 8 hours. Theheat treatment may be conducted in the air or in a hydrogen atmosphere.Preferably, however, the heat treatment is conducted in nitrogen or inan inert gas atmosphere.

The laser treatment is effected by using, as a source of light, anexcimer laser of a wavelength of shorter than 400 nm, or secondharmonics (wavelength of 532 nm) to fourth harmonics (wavelength of 266nm) of YAG or YVO₄ laser. The laser beam is focused into a line or aspot through an optical system and is projected with an energy densityof 100 to 700 mJ/cm²; i.e., the focused laser beam scans thepredetermined region of the substrate to execute the processing. It isfurther allowable to use, instead of the laser, a halogen lamp, a xenonlamp, a mercury lamp or a metal halide lamp as a source of light.

The mechanism of forming the crystalline semiconductor film having ahighly oriented plane {101} of this invention through the above steps,has not yet been clarified but is estimated to be as described below.

First, the crystallization is effected by the heat treatment at 400 to500° C. whereby the metal element reacts with silicon to form a silicidewhich serves as crystalline nuclei that contribute to growing thecrystals. For example, when nickel is used as a representative metalelement, there is formed a nickel silicide (hereinafter written asNiSi₂). The structure of NiSi₂ is that of fluorite in which a nickelatom is arranged between the silicon lattices of the diamond structure.When the nickel atoms are removed from NiSi₂, there remains thecrystalline structure of silicon. It has been known from extensiveexperimental results that the nickel atoms migrate toward the side ofamorphous silicon presumably due to that the degree of solid solution inthe amorphous silicon is higher than that in the crystalline silicon.Therefore, there can be established a model in which nickel formscrystalline silicon while migrating in the amorphous silicon.

NiSi₂ is not particularly oriented. When the amorphous semiconductorfilm has a thickness of 20 to 100 nm, however, the NiSi₂ is permitted togrow only in a direction in parallel with the surface of the substrate.In this case, the energy is the smallest on the interface where theNiSi₂ comes in contact with the plane (111) of crystalline silicon.Therefore, the plane in parallel with the surface of the crystallinesilicon film is a plane (110) and this lattice plane is preferentiallyoriented. When the direction of growth of crystals is in parallel withthe surface of the substrate, and the crystals grow like poles, thereexists the degree of freedom in the rotational direction with thepole-like crystal as an axis, and the plane (110) is not necessarilyoriented. It is therefore considered that other lattice planes mayprecipitate.

In order to enhance the orientation of the lattice plane {101} of thecrystalline semiconductor film, this invention has contrived means forcontaining germanium at a concentration of 0.1 to 10 atomic % as meansfor imposing limitation on the direction of rotation of the pole-likecrystals and for decreasing the degree of freedom.

First, it has been observed that the density of formation of crystallinenuclei decreases when germanium is contained in the amorphous silicon ata concentration of 0.1 to 10 atomic %. FIG. 15 shows the results thereofwherein the density of crystalline nuclei decreases with an increase inthe amount of GeH₄ added at the time of forming the amorphous siliconfilm, i.e., decreases with an increase in the concentration of germaniumtrapped by the amorphous silicon film. When NiSi₂ that is a crystallinenucleus is formed, it is considered that the crystals are growing whileexpelling germanium due to a difference in the interatomic distance.Accordingly, germanium segregates on the outer side of the pole-likecrystals and it is considered that its presence decreases the freedom inthe direction of rotation with the pole-like crystals as axes. As aresult, it becomes possible to obtain a crystalline semiconductor filmhaving a highly oriented plane (110).

Next, described below is a relationship between the conditions offormation and the orientation of crystals observed by the EBSP methodusing the crystalline semiconductor film formed according to theinvention described above. Table 1 shows the conditions for forming theamorphous semiconductor film by the plasma CVD method. Thehigh-frequency electric power is 0.35 W/cm² (27 MHz) which is modulatedinto a pulse discharge of a recurring frequency of 10 kHz (duty ratio of30%) and is fed to the cathode of the plasma CVD device of the flatplate type. Other common conditions include a reaction pressure of 33.25Pa, a substrate temperature of 300° C. and a distance between electrodesof 35 mm.

TABLE 1 Item SGN30 SGN10 SGN5 SN SiH₄ flow rate [sccm] 70 90 95 100GeH₄(H₂ base 10%) [sccm] 30 10  5  0 flow rate RF power [W/cm²] 0.35 ← ←← Pulse frequency [KHz] 10 ← ← ← Duty [%] 30 ← ← ← Pressure [Pa] 33.25 ←← ← Substrate temp (Tsub) [° C.] 300 ← ← ← Gap between [mm] 35 ← ← ←electrodes (GAP)

In order to change the content of germanium relative to silicon, themixing ratio of the flow rate of GeH₄ gas diluted into 10% with SiH₄ andH₂ is changed in a manner that the total flow rate is constant. Underthe conditions described in Table 1, the flow rate of GeH₄ diluted into10% with H₂ is changed to 30, 10 and 5 sccm under the film-formingconditions #SGN30, #SGN10 and #SGN5. The SiH₄ has a purity of not lowerthan 99.9999%, and GeH₄ contains nitrogen and hydrocarbon compounds inamounts of not larger than 1 ppm and CO₂ in an amount of not larger than2 ppm. No GeH₄ is added under the condition #SN. The thickness of theamorphous semiconductor film that is deposited is set to be 50 nm forall samples.

The contents of nitrogen, carbon and oxygen contained in the amorphoussemiconductor film formed under such conditions are measured by thesecondary ionic mass spectrometric method (SIMS). FIG. 13 shows theresults thereof. Samples used for the measurement have films laminatedon the silicon substrate in order of #SN, #SGN5, #SGN 10. Under all ofthese film-forming conditions, the contents of nitrogen and carbon aresmaller than 5×10¹⁸/cm³ and the content of oxygen is smaller than1×10¹⁹/cm³.

The thus formed amorphous semiconductor films are crystallized by usingnickel as a metal element through the heat treatment at 550° C. in anitrogen atmosphere for 4 hours and through the laser treatment. Nickelwas added by using an aqueous solution containing nickel acetate at aconcentration of 10 ppm and by applying it using a spinner. The lasertreatment was conducted by using an XeCl excimer laser (wavelength of308 nm), adjusting the irradiation energy density to be 300 to 600mJ/cm², and at an overlapping ratio of 90 to 95%. The laser treatment iseffected for crystallizing the uncrystallized portions of the filmsubjected to the crystallization through the heat treatment and forrepairing defects in the crystalline particles.

Defects remaining in the crystalline semiconductor film can beeffectively decreased by the hydrogenation treatment to contain hydrogenat a concentration of about 0.01 to 1 atomic %. The hydrogenation can beeffected by the heat treatment at 350 to 500° C. in an atmospherecontaining hydrogen. It is also possible to effect the hydrogenation byusing hydrogen formed by plasma. The film formed by the deposition of afluoride such as SiF₄ or GeF₄ permits fluorine to remain in the film ata concentration of 0.001 to 1 atomic % to compensate for the defects.

FIG. 14 shows the results of evaluating the germanium concentration ofthe thus crystallized #SGN10 and #SGN30 by the SIMS. The content ofgermanium for silicon is 3.5 atomic % in #SGN10 and is 11.0 atomic % in#SGN30. When calculated from the flow rate ratio of GeH₄ relative toSiH₄, germanium is trapped in the film at a ratio 3 to 4 times as largeas silicon. This is because, GeH₄ is decomposed by the glow dischargerequiring energy smaller than the energy required for the SiH₄. It istherefore considered that #SGN5 contains germanium at a concentration ofabout 1.0 atomic %.

FIG. 16 shows the results of measurement of a diffraction peak (220) ofthe same sample by the θ-2θ method. The peak position is 47.466 in thesample #SN and 47.417 in the sample #SGN, indicating a shift in the peakposition due to the addition of germanium.

Details of the crystalline azimuth are found by the EBSP method. FIG. 17is a diagram of back poles of the sample #SN, and FIG. 1 is a diagram ofback poles of the sample #SGN10. From the diagrams of back poles, it isobserved that the plane {101} is strongly oriented in the sample #SGN10shown in FIG. 1. In the sample #SN shown in FIG. 17, on the other hand,orientation is seen on the plane {101} and on a plane {311} midwaybetween the plane {001} and the plane {111}. As reference data, further,FIG. 18 is a diagram of back poles of the crystalline silicon filmformed on a quartz substrate by the heat treatment at 600° C. for 20hours. In this case, it is observed that the plane {111} has beenstrongly oriented.

Table 2 shows the results of orientation ratios of {101}, {001}, {111}and {311} of the samples in a range where the angles of the latticeplanes to the surface of the film are not larger than 5 degrees and in arange where the angles of the lattice planes to the surface of the filmare not larger than 10 degrees based on the diagram of back poles. InTable 2, #HS is the data corresponding to FIG. 18. In this sample, theplanes {311} and {111} are highly oriented, i.e., 18% (not larger than10 degrees) and 12% (not larger than 10 degrees), respectively. In thesample #SN, the planes {101} and {311} are highly oriented. As for theplane {311}, the number of the equivalent lattice planes is larger thanthat of other planes from the standpoint of symmetry. With thepolycrystalline substance oriented in a random fashion, the probabilityof occurrence increases correspondingly.

TABLE 2 (%) {101} {001} {111} {311} Sample 10° 5° 10° 5° 10° 5° 10° 5°#SGN30 7 1 8 2 7 3 19 5 #SGN10 31 14 1 0 3 1 10 3 #SGN5 20 6 1 0 3 0 123 #SN 12 3 1 0 7 2 15 3 #HS 4 1 10 3 12 6 18 4

In the samples #SGN30, #SGN10, #SGN5 to which germanium is added, too, atendency is exhibited, indicating a change in the orientation ofcrystals depending upon the concentration of germanium contained in thefilm. In the samples #SGN10 and #SGN5, what draws a particular attentionis that the lattice plane {101} is strongly oriented compared with otherlattice planes. In the sample #SGN10, the orientation ratio is 31%within the shearing angle of 10 degrees and is 14% even within 5degrees. In the sample #SGN5, the orientation ratio is 20% within theshearing angle of 10 degrees and is 6% within 5 degrees. Such very highorientation ratios for the lattice plane {101} are not accomplished withother samples to which germanium is not added.

In the sample #SGN30, however, when the content of germanium in the filmincreases to 11 atomic %, the orientation ratio on the plane {101}decreases. Therefore, what these results mean is that there exists asuitable range for the concentration of germanium contained in theamorphous silicon film for enhancing the orientation ratio of the plane{101}, and this range of concentration is from 0.1 atomic % to 10 atomic%.

The crystalline semiconductor film exhibiting a high orientationproperty on the lattice plane {101} is obtained not only by addinggermanium at a concentration in a range of from 0.1 to 10 atomic %, butalso by suppressing the concentrations of oxygen, nitrogen and carbon inthe film to be smaller than 1×10¹⁹/cm³, preferably, carbon and nitrogento be smaller than 5×10¹⁸/cm³ and oxygen to be smaller than 1×10¹⁹/cm³,and by selecting the film thickness in a range of 20 to 100 nm so as toproduce such a synergistic effect that the crystals grow dominantly in adirection in parallel with the surface of the substrate.

The crystalline semiconductor film having a high orientation ratio onthe lattice plane {101} can be favorably used as the channel-formingregion of TFTs and as the channel-forming region for determiningproperties of the elements such as photo-electric conversion layer ofphoto-electromotive devices.

Next, described below is an example of fabricating TFTs by using thecrystalline silicon film containing germanium. FIGS. 12A-12C arediagrams illustrating the steps of fabrication of this invention.

In FIG. 12A, a crystalline silicon film 812 containing germanium isformed on a substrate 810. Here, the crystalline silicon film 812 may beany one of those fabricated through the steps of the followingEmbodiments 1 to 4. To fabricate TFTs, the substrate is etched to apredetermined size for element isolation and is divided into islands.When the substrate 810 is a glass substrate, a blocking layer 811 isformed.

The insulating film 813 is used as a gate-insulating film in the TFTsand is formed in a thickness of 30 to 200 nm. The insulating film 813 isa silicon nitride oxide film formed from SiH₄ and N₂O by the plasma CVDmethod or is a silicon nitride oxide film formed from TEOS or N₂O. Inthis embodiment, the former one is selected and is formed maintaining athickness of 70 nm. The insulating film 813 may be formed by a methoddescribed in Embodiment 5.

On the insulating film 813 is formed a gate electrode 814 of anelectrically conducting material containing one or plural kinds ofelements selected from tantalum, tungsten, titanium, aluminum andmolybdenum.

Referring, next, to FIG. 12B, impurity regions 816 are formed forforming source and drain region of the TFT. The impurity regions 816 areformed by the ion-doping method. When the TFT is of the n-channel type,an element of the Group 15 of periodic table as represented byphosphorus or arsenic is added. When the TFT is of the p-channel type,an element of the Group 13 of periodic table as represented by boron isadded.

Thereafter, an interlayer-insulating film 817 is formed by a siliconnitride film or a silicon nitride oxide film relying upon the plasma CVDmethod. The impurity element that is added must be heat-treated at 350to 500° C. for being activated. The heat treatment is effected after theinterlayer-insulating film 817 has been formed to release hydrogencontained in the silicon nitride film or in the silicon nitride oxidefilm so as to be diffused in the crystalline silicon film 812 thatcontains germanium thereby to compensate defects in the crystallinesilicon film with hydrogen. Thereafter, source and drain electrodes 818are formed to obtain the TFT.

The channel-forming region formed of the crystalline silicon filmcontaining germanium and is highly oriented on the lattice plane {101}obtained by the invention, exhibits good interface properties to thegate-insulating film, contains defects at a decreased density on thecrystalline grain boundaries and inside the crystalline particles, andexhibits an electric-field effect mobility. Though the TFT describedabove possessed a single-drain structure, the TFT may be formed having alow-concentration drain (LDD) structure or having a structure in whichthe LDD is overlapped on the gate electrode. The TFTs formed by theinvention can be used as TFTs for fabricating an active matrix liquidcrystal display device and EL display device, and as TFTs for realizinga thin film integrated circuit that substitutes for the LSIs fabricatedby using conventional semiconductor substrates.

EMBODIMENTS

The invention will be described in further detail by way of Embodimentsto which only, however, the invention is in no way limited, as a matterof course.

Embodiment 1

The method of forming the crystalline semiconductor film described withreference to FIGS. 7A-7D are the one that executes the crystallizationby adding a metal element into the whole surface of the amorphoussilicon film containing germanium to assist the crystallization ofsilicon. Referring to FIG. 7A, first, the glass substrate 701 is the onerepresented by the #1773 glass substrate of Coning Co. On the surface ofthe substrate 701, there is formed, as a blocking layer 702, a siliconnitride oxide film by using SiH₄ and N₂O by the plasma CVD methodmaintaining a thickness of 100 nm. The blocking layer 702 is formed sothat alkali metals contained in the glass substrate will not diffuseinto the semiconductor film formed thereon.

The amorphous silicon film 703 containing germanium is formed by theplasma CVD method, and is deposited on the substrate 701 by theglow-discharge decomposition while introducing the GeH₄ gas diluted into10% with SiH₄ and H₂ into the reaction chamber. The detailed conditionscomply with Table 1. However, the conditions employed here are those of#SGN5 or #SGN10 or intermediate conditions thereof. The amorphoussilicon film 703 containing germanium is formed maintaining a thicknessof 50 nm. In order to minimize the contents of impurities such asoxygen, nitrogen and carbon in the germanium-containing amorphoussilicon film 703, use is made of the SiH₄ gas having a purity of notlower than 99.9999% and the GeH₄ gas having a purity of not lower than99.99%. The specifications of the plasma CVD device are such that thereaction chamber has a volume of 13 liters, a composite molecular pumpof an evacuation rate of 300 l/sec is provided in the first stage, a drypump of an evacuation rate of 40 m³/hr is provided in the second stage,to prevent the vapor of organic matters from reversely diffusing fromthe side of the exhaust system, and to enhance the degree of vacuum thatcan be reached in the reaction chamber, so that impurity elements willnot be trapped in the film as much as possible while forming theamorphous semiconductor film.

Referring to FIG. 7B, a nickel acetate solution containing nickel at aconcentration of 10 ppm calculated on the basis of weight is applied byusing a spinner to form a nickel-containing layer 704. Here, in order toimprove compatibility for the solution, the surface of thegermanium-containing amorphous silicon film 703 is treated, i.e., a verythin oxide film is formed by using an ozone-containing aqueous solution,and the oxide film is etched with a mixed solution of hydrofluoric acidand hydrogen peroxide water to form a clean surface, followed by thetreatment with an aqueous solution containing ozone to form a very thinoxide film. The silicon surfaces are hydrophobic in itself and, hence,forming the oxide film makes it possible to uniformly apply the nickelacetate solution.

Next, heat treatment is effected at 500° C. for one hour to releasehydrogen contained in the germanium-containing amorphous silicon film.Then, the crystallization is effected by conducting the heat treatmentat 550° C. for 4 hours. Thus, there is formed a crystallinesemiconductor film 705 as shown in FIG. 7C.

Then, in order to increase the ratio of crystallization (ratio ofcrystalline components in the whole volume of the film) and to repairdefects remaining in the crystalline particles, the laser treatment isconducted, i.e., the crystalline semiconductor film 705 is irradiatedwith a laser beam 706. An excimer laser beam is used having a wavelengthof 308 nm and oscillating at 30 Hz. The laser beam is focused through anoptical system into 400 to 600 mJ/cm², and the laser treatment iseffected at an overlapping rate of 90 to 95%. Thus, there is obtained acrystalline semiconductor film 707 shown in FIG. 7D.

Embodiment 2

Germanium can be added to the amorphous silicon film not only by themethod of forming the film by using gases containing elements asrepresented by SiH₄ and GeH₄ by the plasma CVD method but also by amethod of adding germanium by the ion injection method or the ion-dopingmethod (or is also called plasma-doping method) after the amorphoussilicon film has been formed. In the plasma CVD method, GeH₄ ispreferentially decomposed with the same high-frequency electric powerdue to a difference in the dissociation energy between SiH₄ and GeH₄. Inthis case, unless the film-forming conditions are precisely controlledsuch as employing pulse discharge, a cluster of germanium is formed inthe amorphous silicon film making it difficult to uniformly dispersegermanium.

FIGS. 8A and 8B are diagrams illustrating the steps of adding germaniumby the ion injection method or the ion-doping method. In FIG. 8A, ablocking layer 702 is formed on a glass substrate 701 in the same manneras in Embodiment 1, and an amorphous silicon film 708 is formed thereonmaintaining a thickness of 50 nm. Germanium ions are obtained bydecomposing GeH₄, and are injected into the amorphous silicon film at anacceleration voltage of 30 to 100 keV. The amount of addition ofgermanium is from 0.1 to 10 atomic %. In the ion injection method or theion-doping method, the amount of addition of germanium is correctlycontrolled by controlling the acceleration voltage and the dosage. Uponinjecting germanium having a mass larger than that of silicon, finecrystalline nuclei present in the amorphous silicon film are destroyedmaking it possible to obtain an amorphous semiconductor film which ismore favorable in forming the crystalline semiconductor film.

Thus, there is formed an amorphous silicon film 710 to which germaniumis added as shown in FIG. 8B. Thereafter, a nickel acetate solutioncontaining 10 ppm of nickel on the basis of weight is applied by using aspinner to form a nickel-containing layer 704. Then, the same steps asthose of Embodiment 1 are effected to obtain a crystalline semiconductorfilm 707 as shown in FIG. 7D.

Embodiment 3

Described below with reference to FIGS. 9A-9C is a method of selectivelyforming the metal element that assists the crystallization of theamorphous semiconductor film. In FIG. 9A, a substrate 720 is theabove-mentioned glass substrate or the quartz substrate. When the glasssubstrate is used, a blocking layer is formed in the same manner as inEmbodiment 1.

An amorphous silicon film 721 containing germanium may be formed by theplasma CVD method like in Embodiment 1, or germanium may be introducedby the ion-injection method or by the ion-doping method as in Embodiment2. It is also allowable to employ a method of formation by decomposingSi₂H₆and GeH₄ at a temperature of 450 to 500° C. by the low pressure CVDmethod.

Then, a silicon oxide film 722 is formed maintaining a thickness of 150nm on the amorphous silicon film 721 containing germanium. Though thereis no particular limitation on the method of forming the silicon oxidefilm, the silicon oxide film is formed by, for example, mixing atetraethyl orthosilicate (TEOS) and O₂ together and under the conditionsof a reaction pressure of 40 Pa, a substrate temperature of 300 to 400°C., discharging at a high frequency (13.56 MHz) and an electric powerdensity of 0.5 to 0.8 W/cm².

Next, an opening portion 723 is formed in the silicon oxide film 722,and a nickel acetate solution containing 10 ppm of nickel on the weightbasis is applied. Then, a nickel-containing layer 724 is formed andcomes in contact with the germanium-containing amorphous silicon film721 on only the bottom of the opening portion 723.

The crystallization is effected by the heat treatment at a temperatureof 500 to 650° C. for 4 to 24 hours, e.g., at 570° C. for 14 hours. Inthis case, the crystallization takes place first at a portion of theamorphous silicon film with which nickel is brought in contact and,then, spreads in a direction in parallel with the surface of thesubstrate. The thus formed crystalline silicon film 725 is constitutedby a collection of rod-like or needle-like crystals, each crystalgrowing in a particular direction if viewed macroscopically. Thereafter,the silicon oxide film 722 is removed to obtain the crystalline siliconfilm 725.

Embodiment 4

The metal element used for the crystallization is remaining in thecrystalline silicon film formed according to methods described inEmbodiments 1 to 3. If expressed in terms of an average concentration,the metal element is remaining at a concentration in excess of1×10¹⁹/cm³ though it may not be uniformly distributed in the film. Thesilicon film in such a state can be used as the channel-forming regionof various semiconductor devices inclusive of TFTs. More preferably,however, it is desired to remove the metal element by gettering.

This embodiment deals with a gettering method with reference to FIGS.10A-10C. In FIG. 10A, a substrate 730 is the glass substrate ofEmbodiment 1 or 2, or is the quartz substrate of Embodiment 3. When theglass substrate is used, a blocking layer is formed like inEmbodiment 1. A crystalline silicon film 731 may be formed by any one ofthe methods of Embodiments 1 to 3. A silicon oxide film 732 for maskingis formed maintaining a thickness of 150 nm on the surface of thecrystalline silicon film 731, and an opening portion 733 is formedtherein so that the crystalline silicon film is exposed. In the case ofEmbodiment 3, the silicon oxide film 722 shown in FIG. 9A can be justutilized, and a step of FIG. 9B and the subsequent step may be justtransferred to the steps of this Example. Then, phosphorus is added bythe ion-doping method to form a phosphorus-added region 735 having aconcentration of 1×10¹⁹ to 1×10²²/cm³.

Referring next to FIG. 10B, the heat treatment is effected in a nitrogenatmosphere at 550 to 800° C. for 5 to 24 hours, e.g., at 600° C. for 12hours. Then, the region 735 to which phosphorus is added works as agettering site, and the catalytic element remaining in the crystallizedsilicon film 731 can be segregated in the phosphorus added region 735.

Then, referring to FIG. 10C, the silicon oxide film 732 for masking andthe region 735 to which phosphorus is added are removed by etching, toobtain the crystalline silicon film 736 in which the concentration ofthe metal element used in the step of crystallization is decreased downto smaller than 1×10¹⁷/cm³.

Embodiment 5

This embodiment deals with a method that can be favorably utilized forthe TFTs and the like by decreasing defects in the crystalline particlesor by lowering the level of interface to the insulating film. Acrystalline silicon film 801 containing germanium shown in FIG. 11A maybe the one formed in Embodiment 3. Further, the crystalline silicon film801 containing germanium may be the one subjected to the getteringdescribed in Embodiment 4. In this embodiment, however, the substratemust have a heat resistance of at least about 700 to 1000° C. and,hence, the quartz substrate 801 is employed.

An insulating film 803 on the germanium-containing crystalline siliconfilm 802 is formed of a material containing silicon oxide as a chiefcomponent. For example, a silicon oxide film or a silicon nitride oxidefilm is formed by the plasma CVD method maintaining a thickness of 50nm.

The heat treatment is effected in a state where the insulating film 803is formed in an atmosphere containing halogen (typically chlorine) andoxygen as shown in FIG. 11B. In this embodiment, the heat treatment iseffected at 950° C. for 30 minutes. The treating temperature may beselected in a range of from 700 to 1100° C., and the treating time canbe selected in a range of from 10 minutes to 8 hours.

Due to the heat treatment, an oxide film 804 of about 20 nm is formed onthe interface between the germanium-containing crystalline silicon film802 and the insulating film 803, and a germanium-containing crystallinesilicon film 805 is formed having a decreased thickness. Impurityelements and, particularly, metal impurity elements contained in theinsulating film 803 and in the germanium-containing crystalline siliconfilm 802 in the step of oxidation in a halogen atmosphere, form acompound together with halogen and can, hence, be removed in the gaseousphase. The interface between the oxide film 804 and thegermanium-containing crystalline silicon film 805 obtained through theabove processing, has a low interfacial level density and is veryfavorable.

Embodiment 6

This embodiment deals with a case of forming a CMOS-type TFT bycombining an n-channel TFT 920 and a p-channel TFT 921 in acomplementary manner with reference to FIGS. 19A-19E.

In FIG. 19A, a crystalline silicon film containing germanium is formedon a substrate 901. The crystalline silicon film containing germaniummay be any one formed by the steps of Embodiments 1 to 4. A blockinglayer 902 is formed when the substrate 901 is a glass substrate. Thecrystalline silicon film containing germanium is etched to apredetermined size for element isolation, and island-like semiconductorlayers 903 and 904 are formed.

A first insulating film 905 is utilized as a gate-insulating film forthe TFT, and is formed maintaining a thickness of 30 to 200 nm. Thefirst insulating film 905 is a silicon nitride oxide film formed of SiH₄and N₂O or is a silicon nitride oxide film formed of TEOS and N₂O by theplasma CVD method. This embodiment selects the former film formedmaintaining a thickness of 75 nm. Further, the first insulating film 905may be formed by the method of Embodiment 5.

On the first insulating film 905 are formed gate electrodes 906, 907 ofan electrically conducting material containing one or plural kinds ofelements selected from tantalum, tungsten, titanium, aluminum andmolybdenum.

Referring next to FIG. 19B, phosphorus is doped by the ion-doping methodto form an LDD region in the n-channel TFT 920. Phosphine (PH₃) that isdiluted into 0.1 to 5% with H₂ is used as the doping gas. The dopingconditions will be suitably determined. Here, however, the firstimpurity region 908 formed in each of the semiconductor layers 903 and904 will have an average concentration of from 1×10¹⁷ to 1×10¹⁹/cm³. Atthis moment, the gate electrodes 906 and 907 work as masks againstphosphorus that is doped, and the impurity region 908 is formed in aself-aligned manner.

Referring next to FIG. 19C, a mask 909 is formed by using a photoresist,and is doped again with phosphorus by the ion-doping method. Due to thisdoping, the second impurity regions 910 and 912 have an averagephosphorus concentration of from 1×10²⁰ to 1×10²¹/cm³. Thus, the firstimpurity region 911 formed in the semiconductor layer 903 serves as theLDD region, and the second impurity region 910 serves as source anddrain regions.

In the p-channel TFT 921 as shown in FIG. 19D, a mask 913 is formed byusing a photoresist, and the semiconductor layer 904 is doped withboron. Diborane (B₂H₆) diluted into 0.1 to 5% with H₂ is used as thedoping gas. A third impurity region 914 formed in the semiconductorlayer 904 is added with boron in an amount 1.5 to 3 times as much as thephosphorus concentration for being inverted from the n-type into thep-type, and, hence, has an average concentration of from 1.5×10²⁰ to3×10²¹/cm³. Thus, the third impurity region 914 formed in thesemiconductor layer 904 serves as source and drain regions of thep-channel TFT 921.

Then, an interlayer-insulating film 915 is formed by a silicon nitridefilm and a silicon nitride oxide film formed by the plasma CVD method.Further, the impurity elements that are added must be heat-treated at350 to 500° C. for being activated. The heat treatment is effected afterthe interlayer-insulating film 915 has been formed to release hydrogencontained in the silicon nitride film and in the silicon nitride oxidefilm so as to be diffused in the semiconductor layers 903 and 904 toexecute the hydrogenation, thereby to compensate for the defects in thesemiconductor and in the interface thereof. Further, source and drainelectrodes 916 and 917 are formed to obtain the TFT.

Channel-forming regions 918 and 919 are formed of thegermanium-containing crystalline silicon film which is highly orientedon the lattice plane {101}. Such channel-forming regions have goodinterface properties relative to the gate-insulating film, have adecreased defect density in the crystalline grain boundaries and in thecrystalline particles, and make it possible to obtain a highfield-effect mobility.

Through the above steps, there is obtained a CMOS-type TFT in which then-channel TFT 920 and the p-channel TFT 921 are combined together in acomplementary manner. The n-channel TFT 920 has an LDD region formedbetween the channel-forming region and the drain region, and preventsthe concentration of electric field at the drain terminal. The aboveCMOS-type TFTs make it possible to form a liquid crystal display deviceof the active matrix type or a drive circuit of the EL display device.It is further allowable to apply the n-channel TFT or the p-channel TFTto the transistor for forming pixel portions. It is further possible touse the transistor as the TFT for realizing a thin film integratedcircuit to substitute for the LSIs that have heretofore been produced byusing the conventional semiconductor substrates.

Embodiment 7

Metal elements used for the crystallization are remaining in thecrystalline silicon film formed according to the methods explained inEmbodiments 1 to 3. This embodiment deals with a method of removing themetal element in a manner different from that of Embodiment 4. Themethod consists of removing the metal element by the heat treatment fromthe crystallized silicon film formed by adding the metal element byusing, as a gettering site, a semiconductor film containing a rare gaselement or a semiconductor film to which the rare gas element is added.The method will now be described with reference to FIGS. 23A-23E.

First, a crystalline silicon film which is highly oriented on the plane[101] is obtained by any one of the methods of Embodiments 1 to 3.Reference numeral 2000 denotes a substrate having an insulating surface,and 2001 denotes an underlying insulating film comprising an insulatingfilm such as silicon oxide film, silicon nitride film or silicon nitrideoxide film (SiOxNy). Here, a class substrate is used, and the underlyinginsulating film 2001 is the one of a two-layer structure of a laminateof a first silicon nitride oxide film of a thickness of 50 to 100 nmformed by using SiH₄, NH₃ and N₂O as reaction gases and a second siliconnitride oxide film of a thickness of 100 to 150 nm formed by using SiH₄and N₂O as reaction gases. It is further desired to use a single layerof silicon nitride film as an underlying insulating film 2001. Use ofthe silicon nitride film exhibits the effect as a blocking layer thatprevents the alkali metal contained in the glass substrate fromdiffusing into the semiconductor film that will be formed later, as wellas the effect of enhancing the gettering effect in a gettering step thatwill be effected later. At the time of gettering, nickel tends to moveinto a region of a high oxygen concentration. Therefore, very greateffect is obtained in using the underlying insulating film in contactwith the semiconductor film as the silicon nitride film. It is furtherallowable to use a laminated layer structure in which the siliconnitride oxide film and the silicon nitride film are successivelylaminated. Or, there may be used a three-layer structure in which thefirst silicon nitride oxide film, the second silicon nitride oxide filmand the silicon nitride film are successively laminated.

Next, an amorphous semiconductor film is formed on the underlyinginsulating film by the plasma CVD method, low pressure thermal CVDmethod or sputtering method, followed by the crystallization describedin Embodiment 1 to form a crystalline silicon film 2002 containinggermanium (FIG. 23A).

In this embodiment, the amorphous silicon film containing germanium isformed by the plasma CVD method, the GeH₄ gas diluted into 10% with SiH₄and H₂ is introduced into the reaction chamber, decomposed by glowelectric discharge and is deposited on the underlying insulating film2001. On the surface of the thus obtained germanium-containing amorphoussilicon film is formed a very thin oxide film by using anozone-containing aqueous solution. The oxide film is then removed byetching with a mixed solution of hydrofluoric acid and hydrogen peroxidewater to form a clean surface. Then, a very thin oxide film is formedagain by the treatment with the ozone-containing aqueous solution.Thereafter, a nickel acetate solution containing 10 ppm of nickelcalculated on the basis of weight is applied onto the whole surfacethereof by using a spinner to thereby form a nickel-containing layer.Next, the heat treatment is effected at 500° C. for one hour to releasehydrogen contained in the germanium-containing amorphous silicon film.Then, the heat treatment is conducted in an annealing furnace at 550° C.for 4 hours to effect the crystallization.

The crystallization may be effected by the irradiation with an intenselight from a lamp source of light such as halogen lamp, metal halidelamp, xenon arc lamp, carbon arc lamp, high-pressure sodium lamp or ahigh-pressure mercury lamp in place of the heat treatment using theannealing furnace. When the lamp source of light is used, the lampsource of light for heating is maintained turned on for 60 to 240seconds and, preferably, for 110 to 150 seconds to heat the film at 650to 750° C. and, preferably, at 700° C.

Thus, the amorphous silicon film containing germanium is crystallized toobtain the crystalline silicon film 2002 containing germanium. Duringthe gettering, nickel tends to migrate into a region where the oxygenconcentration is high. It is therefore desired that the oxygenconcentration in the germanium-containing crystalline silicon film 2002is set to be not larger than 5×10¹⁸/cm³.

After the above crystallization, further, the segregated metal elementsmay be removed or decreased with an etchant containing hydrofluoricacid, such as diluted hydrofluoric acid or FPM (mixed solution ofhydrofluoric acid, hydrogen peroxide water and pure water). When thesurface is etched with the etchant containing hydrofluoric acid,further, it is desired to flatten the surface by the irradiation with anintense light from the above lamp source of light.

After the above crystallization, further, the film may be irradiatedwith an intense light such as laser beam or light from a lamp source oflight to further improve the crystallization. The laser beam may be anexcimer laser beam having a wavelength of not longer than 400 nm, or thesecond harmonics or the third harmonics of the YAG laser. After theirradiation with an intense light such as the laser beam or light fromthe lamp source of light for improving the crystallization, thesegregated metal element may be removed or decreased with the etchantcontaining hydrofluoric acid. Or, the surface may be flattened by theirradiation with an intense light from the lamp source of light.

Next, the gettering is effected to remove the metal elements containedin the germanium-containing crystalline silicon film 2002. First, abarrier layer 2003 is formed on the crystalline silicon film containinggermanium. As the barrier layer 2003, there is formed a porous filmwhich permits the metal element (chiefly nickel in this case) to passthrough to the gettering site but which does not permit the etchingsolution used in the step of removing the gettering site to infiltratetherein. Here, there may be used a chemical oxide film formed by thetreatment with ozone water and a silicon oxide film (SiOx). In thisspecification, the film having such properties is particularly referredto as porous film. Further, the barrier layer 2003 may be very thin, andmay be a spontaneously oxidized film or may be an oxide film oxidized bygenerating ozone by the irradiation with ultraviolet rays in anatmosphere containing oxygen.

Next, a semiconductor film 2004 is formed on the barrier layer 2003 towork as a gettering site in a subsequent treatment of gettering (FIG.23B). The semiconductor film 2004 is the one having an amorphousstructure formed by the plasma CVD method, low pressure thermal CVDmethod or, preferably, sputtering method. The semiconductor film 2004has a thickness of 50 to 200 nm and, preferably, 150 nm. In thesubsequent treatment of gettering, nickel tends to migrate into a regionhaving a high oxygen concentration. It is therefore desired that thesemiconductor film 2004 contains oxygen (at a concentration of not lowerthan 5×10¹⁸/cm³ and, preferably, not lower than 1×10¹⁹/cm³ as measuredby the SIMS analysis) to improve the gettering efficiency. There isfurther formed a semiconductor film containing a rare gas element at aconcentration of 1×10²⁰/cm³.

The most preferred method of forming the semiconductor film is such thatsilicon is used as the target by the sputtering method, and a rare gasis used as the sputtering gas. According to the sputtering method, thepressure is decreased at the time of forming the film so that the raregas is easily trapped in the semiconductor film. This makes it possibleto form a semiconductor film containing the rare gas element at aconcentration of 1×10²⁰ to 5×10²¹/cm³ and, preferably, 1×10²⁰ to 1×10²¹/cm³.

The rare gas element is one or plural kinds of those selected from He,Ne, Ar, Kr and Xe. Upon injecting the ions thereof into thesemiconductor film being accelerated in an electric field, it is allowedto form a gettering site while forming dangling bonds and latticedistortions. Among them, it is desired to use the Ar gas which ischeaply available. The treating time for adding the rare gas element maybe as short as about one minute or two minutes, enabling the rare gaselement of a high concentration to be added to the semiconductor film.Therefore, the throughput is strikingly improved compared with thegettering using phosphorus.

In addition to the rare gas element, there may be further added one orplural kinds of elements selected from H, H₂, O, O₂, P and B. Uponadding plural kinds of elements, the gettering effect is obtained in asynergistic way.

Thereafter, the gettering is effected by the heat treatment or by beingirradiated with an intense light from a lamp source of light. When thegettering is to be effected by the heat treatment, the heat treatmentmay be executed in a nitrogen atmosphere at 450 to 800° C. for 1 to 24hours, for example, at 500° C. for 4 hours. Further, when the getteringis to be effected by the irradiation with an intense light from a lampsource of light, the lamp source of light for heating is maintainedturned on for 120 to 300 seconds and, preferably, for 180 seconds toconduct the heat treatment at 650 to 750° C.

Due to the gettering, nickel migrates in the direction of arrows(vertical direction) in FIG. 23D whereby the metal elements are removedfrom the germanium-containing crystalline silicon film 2002 covered bythe barrier layer 2003 or the concentration of the metal elementdecreases. Compared to the gettering using phosphorus, the gettering bythe addition of a rare gas element is very effective, enabling theaddition to be effected at a high concentration, e.g., 1×10²⁰ to5×10²¹/cm³, and, hence, enabling the metal element to be added in anincreased amount for executing the crystallization. That is, uponincreasing the amount of addition of metal element for thecrystallization, the crystallization can be effected in a furthershortened period of time. When the time for crystallization is notchanged, the metal element added in an increased amount makes itpossible to further lower the temperature for crystallization. Uponadding the metal element in an increased amount for the crystallization,further, nuclei are spontaneously generated in decreased amounts and itis allowed to form a favorable crystalline semiconductor film.

After the above gettering treatment, the gettering site 2005 which isthe semiconductor film is selectively removed by etching. The etchingmethod may be dry etching using ClF₃ but not using plasma, or wetetching using an alkali solution such as an aqueous solution containinghydrazine or tetraethylammonium hydroxide (chemical formula,(CH₃)₄NOH)). Here, the barrier layer 2003 works as an etching stopper.The barrier layer 2003 may then be removed with hydrofluoric acid.

Thereafter, the germanium-containing crystalline silicon film is etchedinto a desired shape to form a semiconductor layer 2006 isolated like anisland (FIG. 23E).

FIGS. 24A and 24B show the results of measuring the concentration of ametal element (nickel here) before and after the gettering treatment (bythe total reflection X-ray fluorescence spectroscopy (TXRF)). As shownin FIG. 24B, the TXRF is a measuring method according to which an X-raybeam is permitted to be incident on the surface of the film at a veryshallow angle to detect the X-ray fluorescence emitted by impuritiessuch as metal elements. The TXRF gives data chiefly from a depth of 3 to5 nm from the surface, and makes it further possible to estimate theconcentration of nickel remaining in the crystalline silicon film. Thesensitivity of detection is nearly 10¹⁰/cm².

In FIG. 24A, the ordinate represents the concentration of nickel. Thedata of the sample without the gettering treatment include a value of5×10¹² (arbitrary value). However, the samples subjected to thegettering treatment exhibit smaller values, from which it is learnedthat the nickel concentration in the crystalline semiconductor film isdecreased down to about one-hundredth through the gettering treatment.When the gettering treatments conducted at temperatures of 450° C. and500° C. are compared to each other, it will be learned that the nickelconcentration is lowered more in the case of 500° C.

The germanium-containing crystalline silicon film obtained in thisembodiment is highly oriented on the plane [101] and contains metalelements at concentrations that are sufficiently low in the film, andmakes it possible to lower the off current in the TFT characteristics.

Embodiment 8

The semiconductor device of this invention can be applied to thecircuits to substitute for the display devices and integrated circuitsof a variety of electronic devices and to substitute for theconventional integrated circuits. Such semiconductor devices includeportable data terminals (electronic notebook, mobile computer, cellphone, etc.), video camera, still camera, personal computer, TV andprojector. Their examples are shown in FIGS. 20A to 22D.

FIG. 20A shows a cell phone which comprises a display panel 2701, anoperation panel 2702 and a connection portion 2703, the display panel2701 including a display device 2704, a voice output unit 2705 and anantenna 2709. The operation panel 2702 includes operation keys 2706, apower source switch 2707, a voice input unit 2708, etc. This inventionforms the display device 2704.

FIG. 20B shows a video camera which comprises a main body 9101, adisplay device 9102, a voice input unit 9103, operation switches 9104, abattery 9105 and a picture unit 9106. The invention can be applied tothe display device 9102.

FIG. 20C shows a mobile computer or a portable data terminal which isconstituted by a main body 9201, a camera unit 9202, a picture unit9203, operation switches 9204 and a display device 9205. Thesemiconductor device of this invention can be applied to the displaydevice 9205.

FIG. 20D shows a TV receiver constituted by a main body 9401, a speaker9402, a display device 9403, a receiver unit 9404 and an amplifier unit9405. The invention can be applied to the display device 9403.

FIG. 20E shows a portable notebook constituted by a main body 9501,display devices 9503, a storage medium 9504, operation switches 9505 andan antenna 9506, which is used for displaying data stored in a mini-disk(MD) or in a DVD and for displaying data received by the antenna. Theinvention can be applied to the display devices 9503 and to the storagemedium 9504.

FIG. 21A shows a personal computer constituted by a main body 9601, animage input unit 9602, a display device 9603 and a keyboard 9604. Theinvention can be applied to the display device 9603 and to variousintegrated circuits contained therein.

FIG. 21B shows a player using a recording medium recording a program(hereinafter referred to as recording medium), which is constituted by amain body 9701, a display device 9702, a speaker unit 9703, a recordingmedium 9704 and operation switches 9705. This device uses a DVD (digitalversatile disc) or a CD as a recording medium, with which the user canenjoy appreciating music, movies, or playing games or internet. Theinvention can be applied to the display device 9702 and to variousintegrated circuits contained therein.

FIG. 21C shows a digital camera constituted by a main body 9801, adisplay device 9802, an eyepiece unit 9803, operation switches 9804 anda picture unit (not shown). The invention can be applied to the displaydevice 9802 and to various integrated circuits contained therein.

FIG. 22A shows a front-type projector constituted by a projector 3601and a screen 3602. The invention can be applied to the projector 3601and to other signal control circuits.

FIG. 22B shows a rear-type projector constituted by a main body 3701, aprojector 3702, a mirror 3703 and a screen 3704. The invention can beapplied to the projector 3702 and other signal control circuits.

FIG. 22C is a diagram illustrating structures of the projectors 3601 and3702 in FIGS. 22A and 22B. The projectors 3601, 3702 are constituted byan optical system 3801 of a source of light, mirrors 3802, 3804 to 3806,a dichroic mirror 3803, a prism 3807, a liquid crystal display device3808, a phase difference plate 3809 and a projection optical system3810. The projection optical system 3810 is constituted by an opticalsystem inclusive of a projection lens. Though this embodiment shows anexample of the three-plate type, there may be employed the one of thesingle-plate type without being limited thereto. In the optical pathsindicated by arrows in FIG. 22C, further, the user may suitably providean optical system such as an optical lens, a film having a polarizingfunction, a film for adjusting the phase difference or an IR film.

FIG. 22D is a diagram illustrating the structure of the optical system3801 of the source of light in FIG. 22C. In this embodiment, the opticalsystem 3801 of the source of light is constituted by a reflector 3811, asource of light 3812, lens arrays 3813, 3814, a polarizer/converterelement 3815 and a focusing lens 3816. The optical system of the sourceof light shown in FIG. 22D is only an example, and is not particularlylimited thereto only. For example, the user may suitably provide theoptical system of the source of light with an optical system such as anoptical lens, a film having a polarizing function, a film for adjustingthe phase difference or an IR film.

Though not diagramed, the invention can be further applied as a displaydevice to navigation systems as well as to refrigerators, washingmachines, microwave ovens and fixed telephones. Thus, the inventionfinds a very wide range of applications and can be applied to a varietyof products.

As described above, this invention makes it possible to obtain acrystalline semiconductor film by heat-treating and crystallizing anamorphous semiconductor film containing silicon as a main component andgermanium in an amount of not smaller than 0.1 atomic % but not largerthan 10 atomic % (preferably, not smaller than 1 atomic % but not largerthan 5 atomic %) while adding a metal element thereto, wherein anorientation ratio of the lattice plane {101} is not smaller than 20% andthe lattice plane {101} has an angle of not larger than 10 degrees withrespect to the surface of the semiconductor film, and an orientationratio of the lattice plane {001} is not larger than 3% and the latticeplane {001} has an angle of not larger than 10 degrees with respect tothe surface of the semiconductor film, and an orientation ratio of thelattice plane {001} is not larger than 5% and the lattice plane {111}has an angle of not larger than 10 degrees with respect to the surfaceof the semiconductor film as detected by the electron backscatterdiffraction pattern method.

The TFTs using the crystalline semiconductor film having a highlyoriented lattice plane {101} can be used for fabricating active matrixliquid crystal display devices and EL display devices, and for realizingthin film integrated circuits to substitute for the LSIs that areproduced by using the conventional semiconductor substrates.

1. A thin film transistor comprising: at least a channel forming regionin a crystalline semiconductor film comprising silicon, wherein anorientation ratio of a lattice plane {101} of the crystallinesemiconductor film is not smaller than 20% and the lattice plane {101}has an angle of not larger than 10 degrees with respect to a surface ofthe crystalline semiconductor film, wherein an orientation ratio of alattice plane {001} of the crystalline semicoductor film is not largerthan 3%, and the lattice plane {001} has an angle of not larger than 10degrees with respect to a surface of the crystalline semiconductor film,wherein an orientation ratio of a lattice plane {111} of the crystallinesemiconductor film is not larger than 5%, and the lattice plane {111}has an angle not larger than 10 degrees with respect to a surface of thecrystalline semiconductor film, and wherein the lattice plane {101},{001} and {111} are detected by an electron backscatter diffractionpattern method.
 2. The thin film transistor of claim 1, wherein thecrystalline semiconductor film comprises nitrogen and carbon each at aconcentration smaller than 5×10¹⁸/cm³, and oxygen at a concentrationsmaller than 1×10¹⁹/cm³.
 3. The thin film transistor of claim 1, whereinthe crystalline semiconductor film comprises germanium at aconcentration not less than 0.1 atomic % but not greater than 10 atomic%.
 4. The thin film transistor of claim 3, wherein the crystallinesemiconductor film comprises nitrogen and carbon each at a concentrationless than 5×10 ¹⁸/cm³, and oxygen at a concentration less than1×10¹⁹/cm³.
 5. A transistor according to claim 1, wherein thecrystalline semiconductor film comprises a metal element at aconcentration less than 1×10¹⁷/cm³.
 6. A transistor according to claim1, wherein the crystalline semiconductor film comprises at least a metalelement selected from the group consisting of Fe, Co, Ni, Ru, Rh, Pd,Os, Ir, Pt, Cu and Au.
 7. A transistor according to claim 1, wherein thecrystalline semiconductor film has a thickness in a range of 20 to 100nm.
 8. A transistor according to claim 1, wherein the crystallinesemiconductor film comprises hydrogen or a halogen element.
 9. A thinfilm transistor comprising: at least a channel forming region in acrystalline semiconductor film comprising silicon, wherein anorientation ratio of a lattice plane {101} of the crystallinesemiconductor film is not smaller than 5%, and the lattice plane {101}has an angle of not larger than 5 degrees with respect to a surface ofthe crystalline semiconductor film, wherein an orientation ratio of alattice plane {001} of the crystalline semiconductor film is not largerthan 3%, and the lattice plane {001} has an angle of not larger than 10degrees with respect to a surface of the crystalline semiconductor film,wherein an orientation ratio of a lattice plane {111} of the crystallinesemiconductor film is not larger than 5%, and the lattice plane {111}has an angle of not larger than 10 degrees with respect to a surface ofthe crystalline semiconductor film, and wherein the lattice plane {101},{001} and {111} are detected by an electron backscatter diffractionpattern method.
 10. The thin film transistor of claim 9, wherein thecrystalline semiconductor film comprises nitrogen and carbon each at aconcentration smaller than 5×10¹⁸/cm³, and oxygen at a concentrationsmaller than 1×10¹⁹/cm³.
 11. The thin film transistor of claim 9,wherein the crystalline semiconductor film comprises gemianium at aconcentration not less than 0.1 atomic % but not greater than 10 atomic%.
 12. The thin film transistor of claim 11, wherein the crystallinesemiconductor film comprises nitrogen and carbon each at a concentrationless than 5×10¹⁸/cm³, and oxygen at a concentration less than1×10¹⁹/cm³.
 13. A transistor according to claim 9, wherein thecrystalline semiconductor film comprises a metal element at aconcentration less than 1×10¹⁷/cm³.
 14. A transistor according to claim9, wherein the crystalline semiconductor film comprises at least a metalelement selected from the group consisting of Fe, Co, Ni, Ru, Rh, Pd,Os, Ir, Pt, Cu and Au.
 15. A transistor according to claim 9, whereinthe crystalline semiconductor film has a thickness in a range of 20 to100 nm.
 16. A transistor according to claim 9, wherein the crystallinesemiconductor film comprises hydrogen or a halogen element.
 17. Asemiconductor device comprising: at least a channel forming region in acrystalline semiconductor film comprising silicon, wherein anorientation ratio of a lattice plane {101} of the crystallinesemiconductor film is not smaller than 20%, and the lattice plane {101}has an angle of not larger than 10 degrees with respect to a surface ofthe crystalline semiconductor film, wherein an orientation ratio of alattice plane {001} of the crystalline semiconductor film is not largerthan 3%, and the lattice plane {001} has an angle of not larger than 10degrees with respect to a surface of the crystalline semiconductor film,wherein an orientation ratio of a lattice plane {111} of the crystallinesemiconductor film is not larger than 5%, and the lattice plane {111}has an angle of not larger than 10 degrees with respect to a surface ofthe crystalline semiconductor film, and wherein the lattice plane {101},{001} and {111} are detected by an electron backscatter diffractionpattern method.
 18. The semiconductor device of claim 17, wherein thecrystalline semiconductor film comprises nitrogen and carbon each at aconcentration less than 5×10¹⁸/cm³, and oxygen at a concentration lessthan 1×10¹⁹/cm³.
 19. The semiconductor device of claim 17, wherein thecrystalline semiconductor film comprises germanium at a concentrationnot less than 0.1 atomic % but not greater than 10 atomic %.
 20. Thesemiconductor device of claim 19, wherein tha crystalline semiconductorfilm comprises nitrogen and carbon each at a concentration less than5×10¹⁸/cm³, and oxygen at a concentration less than 1×10¹⁹/cm³.
 21. Adevice according to claim 17, wherein the crystalline semiconductor filmcomprises a metal element at a concentration less than 1×10¹⁷/cm³.
 22. Adevice according to claim 17, wherein the crystalline semiconductor filmcomprises at least a metal element selected from the group consisting ofFe, Co, Ni, Ru, Rh, Pd, Os, Ir, Pt, Cu and Au.
 23. A device according toclaim 17, wherein the crystalline semiconductor film has a thickness ina range of 20 to 100 nm.
 24. A device according to claim 17, wherein thecrystalline semiconductor film comprises hydrogen or a halogen element.25. A device according to claim 17, wherein the semiconductor devicecomprises one selected from the group consisting of a cell phone, avideo camera, a mobile computer, a portable data terminal, a TVreceiver, a portable notebook, a personal computer, a player using arecording medium recording a program, a digital camera, a front-typeprojector and a rear-type projector.
 26. A semiconductor devicecomprising: at least a channel forming region in a crystallinesemiconductor film comprising silicon, wherein an orientation ratio of alattice plane {101} of the crystalline semiconductor film is not smallerthan 5%, and the lattice plane {101} has an angle of not larger than 5degrees with respect to a surface of the crystalline semiconductor film,wherein an orientation ratio of a lattice plane {001} of the crystallinesemiconductor film is not larger than 3%, and the lattice plane {001}has an angle of not larger than 10 degrees with respect to a surface ofthe crystalline semiconductor film, wherein an orientation ratio of alattice plane {111} of the crystalline semiconductor film is not largerthan 5%, and the lattice plane {111} has an angle of not larger than 10degrees with respect to a surface of the crystalline semiconductor film,and wherein the lattice plane {101}, {001} and {111} detected by anelectron backscatter diffraction pattern method.
 27. The semiconductordevice of claim 26, wherein the crystalline semiconductor film comprisesnitrogen and carbon each at a concentration less than 5×10¹⁸/cm³, andoxygen at a concentration less than 1×10¹⁹/cm³.
 28. The semiconductordevice of claim 26, wherein the crystalline semiconductor film comprisesgermanium at a concentration not less than 0.1 atomic % but not greaterthan 10 atomic %.
 29. The semiconductor device of claini 28, wherein thecrystalline semiconductor film comprises nitrogen and carbon each at aconcentration less than 5×10¹⁸/cm³, and oxygen at a concentration lessthan 1×10¹⁹/cm³.
 30. A device according to claim 26, wherein thecrystalline semiconductor film comprises a metal element at aconcentration less than 1×10¹⁷/cm³.
 31. A device accordivg to claim 26,wherein the crystalline semiconductor film comprises at least a metalelement selected from the group consisting of Fe, Co, Ni, Ru, Rh, Pd,Os, Ir, Pt, Cu and Au.
 32. A device according to claim 26, wherein thecrystalline semiconductor film has a thickness in a range of 20 to 100nm.
 33. A device according to claim 26, wherein the crystallinesemiconductor film comprises hydrogen or a halogen element.
 34. A deviceaccording to claim 26, wherein the semiconductor device comprises oneselected from the group consisting of a cell phone, a video camera, amobile computer, a portable data terminal, a TV receiver, a portablenotebook, a personal computer, a player using a recording mediumrecording a program, a digital camera, a front-type projector and arear-type projector.